کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5745662 1412410 2016 16 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Evidence of Mid-ocean ridge and shallow subduction forearc magmatism in the Nagaland-Manipur ophiolites, northeast India: constraints from mineralogy and geochemistry of gabbros and associated mafic dykes
ترجمه فارسی عنوان
شواهدی از مگنتیت پیشرو در فرورفتگی متوسط ​​و کم عمق در افیولیت ناگالند-منیپور، شمال شرقی هندوستان: محدودیت های کانی شناسی و ژئوشیمی گابروها و دایک های مربوط به مافیایی
کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
چکیده انگلیسی

We discuss here the mineralogical and geochemical characteristics of mafic intrusive rocks from the Nagaland-Manipur Ophiolites (NMO) of Indo-Myanmar Orogenic Belt, northeast India to define their mantle source and tectonic environment. Mafic intrusive sequence in the NMO is characterized by hornblende-free (type-I) and hornblende-bearing (type-II) rocks. The type-I is further categorized as mafic dykes (type-Ia) of tholeiitic N-MORB composition, having TiO2 (0.72-1.93 wt.%) and flat REE patterns (LaN/YbN = 0.76-1.51) and as massive gabbros (type-Ib) that show alkaline E-MORB affinity, having moderate to high Ti content (TiO2 = 1.18 to 1.45 wt.%) with strong LREE-HREE fractionations (LaN/YbN = 4.54-7.47). Such geochemical enrichment from N-MORB to E-MORB composition indicates mixing of melts derived from a depleted mantle and a fertile mantle/plume source at the spreading center. On the other hand, type-II mafic intrusives are hornblende bearing gabbros of SSZ-type tholeiitic composition with low Ti content (TiO2 = 0.54 wt.%-0.86 wt.%) and depleted LREE pattern with respect to HREE (LaN/YbN = 0.37-0.49). They also have high Ba/Zr (1.13-2.82), Ba/Nb (45.56-151.66) and Ba/Th (84.58-744.19) and U/Th ratios (0.37-0.67) relative to the primitive mantle, which strongly represents the melt composition generated by partial melting of depleted lithospheric mantle wedge contaminated by hydrous fluids derived from subducting oceanic lithosphere in a forearc setting. Their subduction related origin is also supported by presence of calcium-rich plagioclase (An16.6-32.3). Geothermometry calculation shows that the hornblende bearing (type-II) mafic rocks crystallized at temperature in range of 565°-625 °C ± 50 (at 10 kbar). Based on these available mineralogical and geochemical evidences, we conclude that mid ocean ridge (MOR) type mafic intrusive rocks from the NMO represent the section of older oceanic crust which was generated during the divergent process of the Indian plate from the Australian plate during Cretaceous period. Conversely, the hornblende-bearing gabbros (type-II) represent the younger oceanic crust which was formed at the forearc region by partial melting of the depleted mantle wedge slightly modified by the hydrous fluids released from the subducting oceanic slab during the initial stage of subduction of Indian plate beneath the Myanmar plate.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemie der Erde - Geochemistry - Volume 76, Issue 4, December 2016, Pages 605-620
نویسندگان
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